Research On On-Line Non-destructive Testing System Of Coiled Tubing

Coiled tubing has been widely used in workover and drilling operations. In oilfield applications, Coiled Tubing (CT) is subject to multiple reciprocating plastic bending which causes low cycle fatigue damage on the tubing. This damage is cumulative and leads to eventual failure-loss of pressure and in some cases catastrophic failure. It is so significant and necessity to detect such flaws and wall thinning in coiled tubing before the tubing runs into a well.Based on the ultrasonic testing theory, the overall program of ultrasonic inspection system of coiled tubing was achieved on the analysis of the domestic and foreign technology.Through the computation, the parameters of ultrasonic probe are that chip diameter 6mm, operating frequency 5MHz, inspection recurrence-frequency 1000Hz, probe focal 30mm, eccentricity 5mm and coupling depth 15mm. Ultrasonic coupling system has been designed which contains ultrasonic tank, water circulation system, ultrasonic probe and its adjustment. In the detection process, the circulation system supplies and drains water for ultrasonic tank which takes water as a coupling agent. In actual testing process, the probes position always needs to be adjusted to achieve more favorable testing conditions. The design of ultrasonic probe adjustment can regulate probe eccentricity and coupling depth making echo signal clearer and detection sensitivity higher. In order to detect the displacement of coiled tubing, the photoelectric encoder installed coaxial with the pressing wheel aside the entrance of the ultrasonic tank get the signal of displacement which would be transmitted by optical encoder to the computer. The reflected echo signal is transferred to the computer after the acquisition and processing by the ultrasonic flaw detector which is produced by the probe transmitting ultrasonic to scan the coiled tubing. By the detection analysis software in the computer as soon as the defects is found, the alarm signals is send and control spraying device sprays marking on the position of defects.Single probe simulation test of the designed system was completed. The design of testing model was used to detect longitudinal or transverse defects on the internal and exterior wall and corrosion defects. The results show that the ultrasonic testing technology can achieve higher accurate detection of defects on exterior and internal wall of the coiled tubing, and verify the feasibility of the nondestructive testing system of the coiled tubing.